186 JOURNAL, NATURAL HIST. SOCIETY OF SIAM Vol. I, 
KEY TO THE SPECIES DESCRIBED. - 
The accompanying key will enable anyone, with a little care and 
trouble, to identify all the species described in the previous articles. 
It is entirely an arbitrary key, and is of no value elsewhere. 
Method of using the key. Count the number of costal scales 
across the middle of the body, as shown in the diagram opposite p. 
5 of this volume, and compare it with the color description given. Note 
that the middle of the body is mid-way between the head and the vent, 
and not the head and the tip of the tail. The characters of the scales 
given, although not essential to this list, will be of further assistance. 
The “keel” is a more or less pronounced ridge down the centre of a 
costal scale, and is an important feature in identification. 
